1. Field of the Invention
The present invention relates to an automatic focusing device used for a camera such as a still camera, a video camera, etc., and more particularly to an automatic focusing device having an active range finding system utilizing triangulation combined with a passive range finding system utilizing an image phase difference detecting method for operating the focusing mechanism according to thus obtained range data.
2. Description of the Prior Art
An example of conventional automatic focus adjusting devices is described in Japanese Laid-Open Patent Publication No. 212912/1988 which discloses a device having an active range finding system utilizing triangulation and a passive range finding system utilizing an image phase difference detecting method for operating the focusing mechanism according to thus obtained range data. When the distance to the object cannot be determined by the passive range finding system, a device according to the said invention adjusts the lens focus to a predetermined extent according to the range data obtained through the active range finding system, and then adjusts it once again by the passive range finding system. In other words, the device measures the distance to the object firstly by the passive range finding system. If an image produced using the passive range finding system contains a large degree of blur, which means focusing by the passive range finding system is difficult, the lens is driven, according to the range data obtained through the active range finding system, to a point where focusing by the passive range finding system is possible. If the image produced by the passive range finding system alone has a small degree of blur, focusing is completed immediately by the passive range finding system.
In case of, for example, a 100 mm telephoto lens, the degree of image blur detectable by the phase difference detecting method does not operate satisfactorily at a focus distances near infinity nor very nearby. With the above procedure, however, it is possible to overcome this inadequacy by using the active range finding method to bring the focus into the vicinity of final focus, and then to use the phase difference detecting method for final focus.
The prior-art technique suffers the drawback that the amount of passive range finding data is tremendous when the degree of blur is large. As a result, range calculation, based on highly blurred images requires a long processing time.